C#自动给文章关键字加链接实现代码

/// <summary>
        /// 内联
        /// </summary>
        /// <param name="content"></param>
        /// <returns></returns>
        public string replacetexttag(string content)
        {
            a  a = new a();
            string result = "";
            if (!string.isnullorempty(content))
            {
                //标签
                list<tag> listall = a .gettag(); 获取标签也就是所谓的关键字
                string str1 = content;
                result = keyaddurl(str1, listall);
            }
            return result;
        }
        /// <summary>
        /// 加title，加链接
        /// </summary>
        /// <param name="src"></param>
        /// <param name="keys"></param>
        /// <returns></returns>
        private string keyaddurl(string src, list<topictag> keys)
        {
            regex reg = new regex(@"(?i)(?:^|(?<!<a\b(?>[^<>]*))>)(?>[^<>]*)(?:<|$)");
            int length = 0;
            string temp = string.empty;
            return reg.replace(src, delegate(match m)
            {
                temp = m.value;
                length = temp.length;
                for (int i = keys.count - 1; i >= 0; i--)
                {
                    temp = regex.replace(temp, @"(?is)^((?:(?:(?!" + regex.escape(keys[i].label) + @"|</?a\b).)*<a\b(?:(?!</?a\b).)*</a>)*(?:(?!" + regex.escape(keys[i].label) + @"|</?a\b).)*)(?<tag>" + regex.escape(keys[i].label) + @")",
                        @"$1<a href=""http://cn.greatexportimport.com/topic-" + keys[i].id + @""" target=""_blank"" title=""${tag}"">${tag}</a>");
                    if (length != temp.length)
                    {
                        keys.remove(keys[i]);
                    }
                    length = temp.length;
                }
                return temp;
            });
        }